This invention relates to packages for storing blood and to the method for storing blood in such packages, and more specifically to a package in which the openings are quickly and easily heat sealed by conduction after blood has been introduced into the cavity of the package.
It has long been recognized by personnel connected with the medical and nursing professions that a handy form of package for storing blood for long periods of time is a practical necessity. The discovery that additives such as glycerine can prevent blood cells from becoming damaged when frozen for a long period has increased the demand for suitable packaging.
Ideally, such a package should be provided which is flexible, durable, chemically resistant to its contents, and able to withstand rapid variations along a broad temperature range from, for example, -200.degree. C during freezing to +200.degree. C during sterilization. The material from which the package is formed should be as thin as possible, without losing its strength or durability, so that the contents can be rapidly refrigerated and defrozen. Moreover, equally as important as its physical characteristics, the package after it is filled should be able to be effectively sealed in a quick and uncomplicated way without having to use elaborate and expensive equipment.
Many different types of packaging for storing blood have been developed, but they all include conventional means for sealing the blood within the package, such as cap, plug, or a clamp or the like which are used in conjunction with a port or opening in the package. Seals effected in this way are undesirable in that they are susceptible to being broken if the elements forming the seal are accidently jarred. Blood packages are quite often subjected to less than desirable handling conditions, for example, in military operations, and a tight seal is of primary importance.
Using mechanical refrigeration techniques, temperatures as low as about -80.degree. C can be used, but such procedures require that higher concentrations of glycerol be mixed with the blood in order to protect the red cells. Down as low as -130.degree. C ice crystals may form in the blood which would cause destruction of the cells. Liquid nitrogen cools to temperatures of about -196.degree. C, and at that temperature about 100 mls of protective solution such as glycerol for each 250 ml of red blood cells are used. This is to be contrasted with 400 ml of such protective solution which is required per 250 ml of red blood cells, in the case of mechanical refrigeration at -80.degree. C.
When deep frozen, white cells are damaged. Some at -80.degree. C and even more at -196.degree. C. These, however, can be washed out. Aluminum vessels have been used for this operation and later stainless steel was used, but such metals are not suitable for centrifugation. They obviously are not transparent and so the operator cannot observe for contaminants. To meet this problem a plastic transparent bag has been sought for many years. Polyvinylchloride has been used at temperatures of -4.degree. C but at lower temperatures such as those mentioned above maintained by mechanical refrigeration (-80.degree. C), the PVC is brittle. PVC cannot be used at all at -196.degree. C because it is much too brittle.
An object of the invention, therefore, is to obtain a package containing a suspension of cellular components of blood which can be used for washing and centrifuging such suspension, as well as sterilizing and deep freezing the suspension, all in the same package.